Thanks for the link @pphoto. Yes, you are right that the color picker is an objective tool to help you match the colors of two pictures. I just don’t think this is an either or situation. It would be great to be able to have both pictures side by side, and still use the color picker to match colors without having to switch back and forth.
Something like this is what I mean:
I don’t know how easily this could be implemented, or if this would be the best solution, but it would be enough for me.